The present invention relates generally to optical switching devices and, more particularly, to a circular grating resonator structure with integrated electro-optical modulation.
Multi-core microprocessor architectures have been developed in order to mitigate increased power dissipation in high-performance computer chips. However, the bandwidth limitations for global electrical interconnections between various cores are rapidly becoming the major factor in restricting further scaling of total chip performance. One approach resolving this interconnect bottleneck is to transmit and route signals in the optical domain, since optical signals can provide both immense aggregate bandwidth and large savings in on-chip dissipated power.
Many existing types of optical switches fall under the category of microelectromechanical (MEMS) devices, in which tiny components such as prisms or mirrors are positionally adjusted in order to redirect input optical signals. However, such MEMS devices are not suited for multi-core chip scaling purposes. On the other hand, the field of integrated optics has expanded tremendously in recent years, and integrated optical device solutions are now being proposed for applications in a variety of fields including, for example, telecommunications, data communications, high performance computing, biological and chemical sensing, and radio frequency (RF) networks.
In this regard, an optical waveguide or combination of optical waveguides may be formed on an integrated circuit (IC) to form devices such as optical resonators, arrayed waveguide gratings, couplers, splitters, polarization splitters/combiners, polarization rotators, Mach-Zehnder (MZ) interferometers, multimode interference waveguides, gratings, mode transformers, delay lines, and optical vias. Such on-chip devices may in turn be used to create an integrated optical circuit or planar light wave circuit that performs one or more optical functions such as, for example: multiplexing/demultiplexing, optical add/drop, variable attenuation, switching, splitting/combining, filtering, spectral analysis, variable optical delay, clock distribution, amplitude/phase modulation, polarization rotation, comb generation, and dispersion compensation.
Circular grating resonators (CGRs), also known as Annular Bragg reflectors or “fingerprint” structures have more recently been considered for applications in integrated optics such as lasing and all-optical switching. In particular, CGRs have a very small footprint of a few micrometers, which essentially corresponds to the smallest optical resonators possible. Thus, even at relatively low refractive index contrasts, CGRs offer full two-dimensional light confinement, making circular grating resonators a very attractive candidate for future integrated photonic devices since they may be fabricated of any transparent (low absorption) material.
With respect to electro-optical devices in which the resonance of the optical modulator is adjusted by an electrical control signal, there must be a technical means of applying an electric field in the region of the resonator. The electric field changes the index of refraction of the resonator and hence its resonance frequency. In so doing, an input optical signal to the resonator may be switched on and off. However, the incorporation of electrodes into a photonic structure such as a CGR is a significant challenge, since electrically conducting materials absorb light and thus lead to high losses.